Brain oscillatory 4-35 Hz EEG responses during an n-back task with complex visual stimuli.

Brain oscillatory responses of 4-35 Hz EEG frequencies elicited during performance of a visual n-back task with complex visual stimuli were assessed in 20 adult volunteers. Spectral power changes were assessed separately for target and non-target stimuli in four different memory load conditions (0, 1, 2, and 3-back). The presentation of both target and non-target stimuli elicited long-lasting ~4-8 Hz power increases, which were more prominent at the beginning of stimulus onset during presentation of target stimuli, as compared to non-target stimuli, in the 0-back memory load condition. ~8-25 Hz power decreases appeared at stimulus onset. These power decreases were more prominent during the presentation of target stimuli, as compared to non-target stimuli, and their duration increased as a function of memory load between the 0-, 1-, and 2-back, but not the 3-back, memory load conditions. The current results provide further evidence in support of the notion of a complex interplay between both ~4-8 Hz power increases and ~8-25 Hz power decreases during cognitive memory task performance.